In an electrophotographic printing machine, a photoconductive member, such as a photoreceptor, is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoreceptor is thereafter selectively exposed. Exposure of the charged photoreceptor dissipates the charge thereon in the irradiated areas. This records an electrostatic latent image on the photoreceptor corresponding to the informational areas contained within the original document being reproduced. After the electrostatic latent image is recorded on the photoreceptor it is “developed.” The development process deposits toner in the same pattern as the latent image on the photoreceptor. This developed toner is subsequently transferred to a print sheet. The sheet is then heated to permanently affix the toner image thereto in image configuration.
The electrostatically attractable developing material commonly used in developing systems comprises a pigmented resinous powder referred to here as a “toner” and a “carrier” of larger granular carrier particles formed with iron, steel, or ferrite cores coated with a material removed in the triboelectric series from the toner, so that a triboelectric charge is generated between the toner powder and the granular carrier. The toner is attracted to the electrostatic latent image from carrier bristles to produce a visible powder image on an insulating surface of the photoreceptor.
In a practical application, however, some carrier particles will adhere to the photoreceptor after an area of the photoreceptor leaves the development zone. These adhering carrier particles prevent intimate contact between the support surface (e.g., a sheet of paper) and the toner particles, and they may affect the quality of the copy produced. In addition, because such adhering carrier particles are hard, they may abrade the surface of the photoreceptor if not removed prior to reaching the cleaning zone. Consequently, it is desirable that all such carrier particles be removed from the photoreceptor with each cycle of the photoreceptor.
Many designs of xerographic printers and copiers use what will here be called “customer-replaceable units” or CRUs, or more generally “cartridges.” Typically a CRU will include a photoreceptor and ancillary hardware, such as a corotron or equivalent charge device and a cleaning station. The CRU is designed to be easily removed from the larger machine and replaced with an effectively new CRU. Used CRU's can in various ways be remanufactured, such as by cleaning the CRU, replacing spent parts such as the photoreceptor, and refilling the CRU with a new supply of marking material. The present disclosure relates to a carrier particle pickoff device suitable for inclusion in a CRU.